Previous studies have shown that a gel composed a calf skin collagen, CaC12 and K2HPO4 can induce hard connective tissue into pulpless open apex teeth in Rhesus monkeys. The purpose of this study was to determine if this gel, cross-linked in glutaraldehyde, would support connective tissue growth into debrided root canals. Thirty maxillary and mandibular incisor teeth, 20 partial pulpectomies and 10 total pulpectomies, were done in incisors of 6 Rhesus monkeys. One half of each procedural group was filled with collagen-calcium phosphate gel and one half and CaOH-saline paste to serve as controls. Animals were killed at time periods ranging from 3 to 8 months. Block sections of bone containing the teeth were removed and prepared for histologic examination. Sections showed hard tissue forming within root canals of 13 teeth filled with collagen-mineral gel. Nine of 15 control teeth resulted in hard tissue formation adjacent to the CaOH-saline paste. Collagen-CaPO4 gel cross-linked with glutaraldehyde appears to induce more complete regeneration of connective tissue within debrided root canals than CaOH-saline paste.